A prospective, open-label trial of 6-thioguanine in patients with ulcerative or indeterminate colitis.

6-thioguanine (6-TG) has emerged as a promising therapeutic alternative in patients with Crohn's disease intolerant or resistant to azathioprine (AZA) and/or 6-mercaptopurine (6-MP). The aim of the present study was to evaluate the safety and efficacy of 6-TG in patients with ulcerative colitis (UC) or indeterminate colitis (IC) intolerant or resistant to AZA/6-MP. Twenty patients with an acute flare, steroid-dependent or steroid-refractory disease attending our outpatient department were included in the study. Measurement of 6-TG nucleotide levels was done to check compliance. Complete, partial and non-response were defined by means of the clinical activity index and the daily steroid demand. Secondary outcome parameters included changes in cumulative steroid doses, C-reactive protein (CRP) levels, and an endoscopic score. Out of 20 patients 4 were excluded owing to noncompliance; 2/16 compliant patients (13%) had to be prematurely withdrawn because of adverse events, which ceased upon drug discontinuation. By per-protocol analysis, 5/14 patients (36%) were complete, 6/14 (43%) partial and 3/14 (21%) non-responders. In addition to the reduction of the cumulative steroid dose over 3 months, CRP decreased in the study population and the endoscopic score decreased in treatment responders. Treatment with 6-TG was effective in patients with UC or IC previously intolerant or resistant to AZA/6-MP. Future work is needed to define a subpopulation of patients at low risk for its potential hepatotoxicity, which we assume will benefit from 6-TG.